Rapid Design and Navigation Tools to Enable Small-Body Missions

The goals of this research project have been to lay the groundwork for and develop prototype rapid design and navigation tools that together provide significant improvement in how quickly and efficiently small body missions are planned. The resulting methods and tools provide: •A fast design space search for complex trajectories to primitive bodies which o Take advantage of gravity assist flybys and include maneuvers o Provide flybys of and/or rendezvous with multiple bodies o Efficiently search through many possible target bodies and many different sequences •Improved understanding of proximity operations and science trajectories around small bodies, through o Parameterizing and classifying the design space for trajectories around small bodies o A detailed new understanding and modeling of heliotropic orbits The work was divided into essentially two parts: A) Path Planning For Trajectories to Small Bodies In the first section, the state-of-the-art in path planning for spacecraft trajectories with multiple flyby bodies has been advanced. These new methods enhance ability to find desirable interplanetary trajectories quickly: • Incorporation of performance indices for relative search tree pruning in the trajectory search process, speeding up the search process (See Figure 1) • Automated methods for including v∞ leveraging maneuvers and nπ transfers in integrated multiple-flyby trajectory searches (See Figure 1 and Figure 2.) • Included small body rendezvous as part of the trajectory search to improve the ability to plan multi-target missions, including sample returns. • The new methods have been included as new capabilities in the existing software called Explore, a preliminary search tool for spacecraft trajectories. The tool implements in a robust manner the new algorithms developed in this grant. (See Figure 1 and Figure 2.) B) Trajectory design space around small bodies: This portion of the research investigated proximity operations near small bodies, in particular oblate asteroids subject to large solar radiation pressures. • Investigated stability regions and the perturbation environment around small bodies using a fast Lyapunov indicator, comparing preliminary results to previous literature and to known periodic orbit solutions. (See Figure 3.) • Mapped new frozen orbit families around a large class of asteroids that are heavily perturbed by solar radiation pressure and the J2 oblateness term. • Heliotropic orbits are a special class of low-altitude, long-lifetime orbits that leverage solar radiation pressure and body oblateness to maintain orbit shape (See Figure 4). In this project, we made the first investigation of these types of orbits for primitive body orbiters. (in the past these orbits were considered in the context of dust dynamics at high altitudes of planetary atmospheres). • Developed a method for determining inclined heliotropic orbits around a body using doubly-averaged dynamics. This double averaging technique is new, and allows for the first time, analytical descriptions of 3D heliotropic orbits • Investigated effect of high degree gravity terms, shadowing, and uncertainty on heliotropic orbits • A detailed analysis of frozen and heliotropic orbits at Bennu was performed and documented, in efforts to aid the upcoming (exciting) OSIRIS-REx mission.